Study of adhesive bondlines in modified wood with fluorescence microscopy and X-ray micro-computed tomography

The quantitative penetration of three coldset wood adhesives [one-component polyurethane (PU), emulsion polymer isocyanate (EPI), poly (vinyl acetate) (PVAc)] under hydraulic pressure into different types of modified wood was studied using fluorescence microscopy and the results were compared to these of a previous study without pressure on adjacent wood samples. The effective penetration (EP) of PU was negatively affected by furfurlylation and NMM modification when pressure was applied. For PVAc, 30% NMM treatment and heat treatment of Scots pine and beech at 210 degrees C had a negative effect on its EP, but against this the EP of this adhesive increased after heat treatment of beech at 195 degrees C. In the case of furfurylation, the depth of penetration of all adhesives was less into wood treated with higher concentration of furfuryl alcohol. PU showed a much deeper penetration into NMM-modified and heat treated wood than the other adhesives with the exception of heat-treated beech at 195 degrees C. Application of pressure led to rather different results as compared to the EP data when no pressure was applied. The three-dimensional (3D) visualisation of the penetration of PU adhesive into heat-treated Scots pine was also examined by X-ray micro-computed tomography (X mu CT). The 3D flow pattern of PU adhesive into heat-treated Scots pine was clearly depicted by X mu CT. (C) 2016 Elsevier Ltd. All rights reserved.